1. Field of the Invention
The present invention relates to a method of controlling a light intensity in an image exposure apparatus, and more specifically, to a method of controlling a light intensity in an image exposure apparatus that carries out what is called xe2x80x9cexposure using comb light beam spotsxe2x80x9d.
2. Description of the Related Art
Currently, there are types of image exposure apparatus that expose an image onto an exposure surface by what is called xe2x80x9cexposure using comb light beam spotsxe2x80x9d (see Japanese Patent Application Publication (JP-B) No. 8-12335 and the like). In an image exposure apparatus by the exposure using comb light beam spots, the positions of light sources are set in advance such that the intervals, in the sub-scanning direction, between beams of light which are exposed by one main scan are each an integer multiple of the intervals between main scanning lines (intervals in the sub-scanning direction) of an image formed on an exposure surface. Then, in the first main scan, main scanning lines are main-scanned at fixed intervals. By carrying out sub-scanning at a predetermined feed amount and then carrying out the next main scan, main scanning lines of the second time or times thereafter are subsequently placed between the first main scanning lines. (In JP-B No. 8-12335, such an exposure method is referred to as an xe2x80x9coverlapping modexe2x80x9d.) By carrying out the main scanning a plurality of times together with the sub scanning at the predetermined feed amount in the manner described above, the final main scanning lines are structured so as to form the final image.
In carrying out the exposure using comb light beam spots described above, the feed amounts in the sub-scanning direction must be precisely identical in each sub-scan. Otherwise, certain main scanning lines approach each other such that the entire intensity of light at that portion is increased, or conversely, certain main scanning lines move away from each other such that the entire intensity of light at that portion is decreased. As a result, the light intensity distribution becomes non-uniform.
However, it is difficult to make the feed amounts in the sub-scanning direction precisely identical. Further, depending on the configuration of the expose surface and the like, even when the feed amounts in the sub-scanning direction are made precisely identical, there may be cases in which the intervals between the main scanning lines on some parts of the exposure surface are not constant.
In view of the aforementioned, an object of the present invention is to obtain a method of controlling a light intensity in an image exposure apparatus in which a high-precision image can be exposed by reducing nonuniformity in intensity of light even when there is an error in a feed amount in a sub-scanning direction in an image exposure apparatus that utilizes exposure using comb light beam spots.
In a first aspect of the present invention, there is provided a method of controlling a light intensity in an image exposure apparatus which includes: light sources of a number m which emit light in accordance with image information, the light sources being aligned along a fixed direction so as to be disposed at intervals which are n times a line interval L which is a line interval between main scanning lines on an exposure surface, n being a natural number; and scanning means for carrying out main scanning by relatively moving the m light sources with respect to the exposure surface in a direction perpendicular to the direction in which the light sources are arranged, and for carrying out sub-scanning by relatively moving the m light sources with respect to the exposure surface in the direction in which the light sources are arranged by a feed amount of (Lxc3x97m), the method comprising the step of: in a case in which an interval between specific main scanning lines is made larger or smaller than the line interval L due to an error in a feed amount in the sub-scanning direction, when another main scanning is carried out, controlling the intensity of light of a light source, among the m light sources, which corresponds to the portion in which the interval between the main scanning lines is made larger or smaller.
With the structure described above, according to the first aspect of the present invention, so-called exposure using comb light beam spots can be carried out. Namely, although there are intervals of (Lxc3x97n) between a plurality of main scanning lines that are formed by one main scanning, the intervals are filled in by carrying out sub-scanning at the feed amount of (Lxc3x97m) and further carrying out the next main scanning. By carrying out the above operation xe2x80x9cnxe2x80x9d times, main scanning lines are ultimately formed at fixed line intervals L so that an image is exposed. Since, in the method of controlling a light intensity in an image exposure apparatus of the first aspect, m and n are relatively prime and m greater than nxe2x89xa72, the main scanning lines do not overlap each other and the lines to be main-scanned are men-scanned without fail.
When there is an error in a feed amount in the sub-scanning direction, specific mail scanning lines approach or move away from each other. However the intensity of light of a light source, which corresponds to the portion at which the specific main scanning lines approach or move away from each other, is controlled when another sub-scanning is carried out. Accordingly, when exposure of the entire exposure surface is completed, nonuniformity in the intensity of light in the sub-scanning direction is eliminated, thereby allowing a high-precision image to be obtained.
According to a second aspect of the present invention, in the method of controlling a light intensity in an image exposure apparatus of the first aspect, m and n are relatively prime and are set so as to satisfy the relation m, nxe2x89xa72.
The condition of main scan is thus set in the manner described above, and therefore, the main scanning lines do not overlap each other and the lines to be main-scanned are main-scanned without fail. Accordingly, main scanning of a desired main scanning line can reliably be carried out.
In a third aspect of the present invention, there is provided a method of controlling a light intensity in an image exposure apparatus which includes: light sources of a number m which emit light in accordance with image information, the light sources being aligned along a fixed direction so as to be disposed at intervals which are n times a line interval L which is a line interval between main scanning lines on an exposure surface, n being a natural number; and scanning means for carrying out main scanning by relatively moving the m light sources with respect to the exposure surface in a direction perpendicular to the direction in which the light sources are arranged, and for carrying out sub-scanning by relatively moving the m light sources with respect to the exposure surface in the direction in which the light sources are arranged by a feed amount of (Lxc3x97(mxe2x88x92a)), (a is a natural number), m and n being not relatively prime and (mxe2x88x92a) and n being relatively prime, and satisfying the relation (mxe2x88x92a)xe2x89xa7(mxc3x97n)/2, the method comprising the step of: in a case in which an interval between specific main scanning lines is made larger or smaller than the line interval L due to an error in a feed amount in the sub-scanning direction, when another main scanning is carried out, controlling the intensity of light of a light source, among the m light sources, which corresponds to the portion in which the interval between the main scanning lines is made larger or smaller.
With the structure described above, according to the third aspect of the present invention, so-called exposure using comb light beam spots can be carries out. In other words, there are intervals of (Lxc3x97n) between plural main scanning lines which are formed by one main scanning, and the intervals are filled in by carrying out sub-scanning at the feed amount of (Lxc3x97(mxe2x88x92a)) and further carrying out the next main scanning. By carrying out the above operation xe2x80x9cnxe2x80x9d times, main scanning lines are ultimately formed at fixed line intervals L so that an image is exposed.
When there is an error n a feed amount in the sub-scanning direction, specific main scanning lines approach or move away from each other. However, the intensity of light of a light source, which corresponds to the portion at which the specific main scanning lines approach or move away from each other, is controlled when another sub-scanning is carried out. Accordingly, when exposure of the entire exposure surface is completed, nonuniformity in the intensity of light in the sub-scanning direction is eliminated, thereby allowing a high-precision image to be obtained.
In the first to third aspects of the present invention, a specific structure for eliminating nonuniformity in intensity of light which is caused by an error in a feed amount in the sub-scanning direction is shown. For example, there are cases, as shown in a fourth aspect of the present invention, in which specific main scanning lines approach each other due to the error. In such cases, since the intensity of light increases between the main scanning lines that approach each other, when another main scanning is carried out (i.e., when this position is main-scanned), the intensity of light of the corresponding light source is decreased.
In contrast, there are also cases, as shown in a fifth aspect of the present invention, in which specific main scanning lines move away from each other due to the error. In such cases, since the intensity of light decreases between the main scanning lines that move away from each other, when another main scanning is carried out (i.e., when this posit on is main-scanned), the intensity of light of the corresponding light source is increased.
In a sixth aspect of the present invention, in any of the first to fifth aspects, the image exposure apparatus comprises a memory in which the error is stored in advance in correspondence with the exposure surface, and on the basis of the error that is stored in the memory, the intensity of light of a specific light source of the m light sources is controlled when sub-scanning is carried out.
In this way, errors are stored in advance in the storing means of the image exposure device, and the light intensity of the specific light source is controlled on the basis of the error. Thus, control of the light intensity is facilitated.